Subsea protective covering

ABSTRACT

A protective covering for subsea well apparatus is provided. The covering is generally a pyramidal structure and includes blades at the corners extending below the base of the structure. The blades are sized to prevent snaring of objects dragged over the covering. The covering may be assembled from sections after transport over a public highway. Methods for transporting and installing the covering and achieving penetration of the blades into the seafloor are also provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to subsea drilling and productionoperations. More particularly, the invention relates to apparatus formechanically isolating equipment on the seafloor and methods for placingthe apparatus on the seafloor and over the equipment to be isolated.

[0003] 2. Description of Related Art

[0004] Fish harvesting operations and production of oil and gas co-existin many offshore areas of the world. If a well is temporarily abandonedin a water-covered area and the depth of the water is such thatcommercial fishing gear may be affected by the presence of a wellapparatus extending above the seafloor, a subsea covering over the wellis needed. In the U.S. Gulf of Mexico Outer Continental Shelf Region,according to 30 C.F.R. 250.703(b), when a subsea covering is used toprotect a casing stub or other equipment, the subsea covering must allowcommercial fishing gear to pass over the covering without causing damageto the covering, the casing stub or other equipment, or the fishinggear. Approval may be required from a government agency to install asubsea protective covering over a well.

[0005] To ensure that a subsea protective covering is effective and doesnot pose a hazard or conflict with other uses of the outer continentalshelf of the United States, operators are required to perform a“trawling test.” In this test a trawling boat pulls a net across thesubsea protective covering. The net is dragged over the device asufficient number of times and in a sufficient number of directions toensure 100 per cent coverage of all potential device impediments.Impediments may include edges and corners, anchoring equipment, eyeletsor other attachments to the subsea protective covering. A description ofthe trawling operation and the nets that were used is then reported to agovernment agency within thirty (30) days after completing the trawlingtest.

[0006] To confirm that the subsea protective covering remains properlyinstalled, a visual inspection or trawl test must be performed at leastannually. The test may be waived if the proposed design and installationmethod for the protective covering have proven to be successful in thepast and government agency approval is requested and granted.

[0007] U.S. Pat. No. 5,259,458 discloses a subsea abandoned wellheadprotection structure that can be installed by lowering and centering thestructure over a wellhead while the structure is attached to drill pipe.Downward-directed jets around the periphery of the base area of thestructure allow the seafloor to be excavated around the base by pumpingfluid through the structure and out the jets. This arrangement isdesigned to cause the structure to be embedded in the seafloor. If it isevenly embedded so that none of the base is exposed above the seafloor,then nets or other fishing equipment would not become snared by thestructure.

[0008] Although an embedded subsea protective covering should pose noproblems, events can prevent proper placement and maintenance of theposition of the covering. The seafloor may be uneven. Water currents maycause erosion of the seafloor around the base. If a jetting process isused to place the protective covering, the jetting may producenon-uniform penetration, leaving exposed areas of the base of thestructure. What is needed is a subsea protective covering that will notbe snared by nets or other commercial equipment passing over thestructure even if the covering is not completely or uniformly embeddedin the seafloor. There is also a need for a protective covering that maybe transported to a well site in sections, so that it can be transportedat minimum cost over public highways.

DESCRIPTION OF THE FIGURES

[0009]FIG. 1 shows a partial cutaway side view of a preferred embodimentof the subsea protective covering.

[0010]FIG. 2 shows a partial cutaway top view of the embodiment shown inFIG. 1.

[0011]FIG. 3(a) shows a detail top view of the cap of the protectivecovering of FIG. 1.

[0012]FIG. 3(b) shows a detail side view of the cap of the protectivecovering of FIG. 1.

[0013] FIGS. 4(a), 4(b) and 4(c) show side, end and top views,respectively, of the protective blade of this invention.

[0014]FIG. 5 illustrates installation of the subsea protective coveringover a subsea wellhead.

SUMMARY OF THE INVENTION

[0015] A protective covering for subsea apparatus is provided thatincludes blades that extend below the corner support members of thecovering. The blades prevent snaring of fishing or other equipment onthe corners of the protective covering. The covering may be installed bydrill pipe, and a television camera deployed by wireline through thedrill pipe may be used to guide the covering to a selected location. Abumper sub in the drill pipe may be used to drive the blades into theseafloor. The covering may also be installed by cable.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] Referring to FIG. 1, a partial cut-away side view of subseaprotective covering 10 is shown. Covering 10 includes skin 12, which ispreferably steel plate. The thickness of the plate is preferably in therange from about {fraction (3/16)}-inch to about ½ inch. Skin 12 ispreferably welded to all slanted support members, which include lateralslanted support members 13 and 15 and corner slanted support members 14.Bottom horizontal members 16 form a base, while intermediate horizontalmembers 19 may be used to add strength to covering 10. Lateral slantedsupport member 15, positioned where covering 10 may be divided intosections, consists of parts, 15A and 15B, which may be flanged together.Skin 12 and bottom horizontal members 16 may also be flanged where theyintersect a lateral slanted support member that is flanged and skin 12may be attached at each flange, such that protective covering 10 can beassembled in a plurality of sections. Cap 18 is preferably attached toall slanted support members. Cap 18 may include an attachment point forplacing protective covering 10 on the seafloor. Blade assembly 20 ispreferably attached to base 16 and corner slanted support members 14 ateach corner. Blade assembly 20 and cap 18 will be described in moredetail below.

[0017] The overall height of covering 10 is selected to cover a casingstub or mudline suspension or any other equipment that is to bemechanically protected. The dimensions of covering 10 may be in therange of about 14 to 20 feet square at the base with a height usually inthe range from about 7 feet to 10 feet. A height in the lower part ofthis range may be needed for covering a stub of 30-inch casing extendingabove the seafloor, for example. An anode for corrosion protection maybe attached if the covering is to be left subsea for an extended time.

[0018]FIG. 2 illustrates a partial cutaway top view of subsea protectivecovering 10. Lateral slanted support members 15A and 15B are boltedtogether and may be separated for transport of covering 10. This is agreat advantage when covering 10 is to be transported by highway to adock for deployment subsea. The maximum width without escort along apublic highway can sometimes be achieved by separating the covering. Themaximum width with escort can be used to allow a greater spread distanceof a covering by separating it and re-assembling it at the dock.

[0019] Although four corners are shown in the drawings herein, eachcorner forming a 90-degree angle in a horizontal plane, it should beunderstood that any structure having a polygonal base and sides whichform the bases of triangular surfaces meeting at a common vertex may beused. The number of base corners may vary from three to ten or more.Lateral slanted support members may or may not be used, but a cornerslanted support member will normally be present at each corner.

[0020]FIG. 3(a) illustrates a top view and FIG. 3(b) illustrates across-section view of cap 18. Drill pipe connector 30 is joined to topplate 34 by cap support members 32 and 36. Lateral slanted supportmembers 15 are welded to top plate 34. Connector 30 is preferablyadapted to receive drill pipe or other pipe to be used for deployingcovering 10 on the seafloor. Alternatively, connector 30 is a hook orother means for lowering covering 10 to the seafloor by cable.

[0021] FIGS. 4(a), 4(b) and 4(c) illustrate details of blade assembly20. Blade 40 is attached to blade support 42. Support 42 is adapted toattach to bottom horizontal support members 16 and corner slantedsupport members 14 (FIG. 1) as an extension in the direction of supportmembers 14. Blade 40 may be directly attached to corner slanted member14 or bottom horizontal member 16 at the corners of covering 10 bywelding or may be attached through support 42 and bolts (not shown)placed through bolt holes 48. The extension of skin 12 and cornerslanted support members 14 by blade 40 prevents snaring of a net orother object that is dragged over covering 10. Alternatively, blade 40may be at a slope angle different from the slope angle of corner support14 and still achieve the purpose of preventing snaring on the covering.For example, blade 40 may be at a slope angle that is about 30 degreesless than the slope angle of corner support 14. (Vertical is zero slopeangle.) Also, blade 40 may be at a greater slope angle than cornersupport 14. Blade 40 may have sloping surfaces 50 positioned at thebottom to allow easier penetration of the blade into the seafloor. Blade40 may be formed from steel plate and may have a thickness in the rangeof about 0.5 inch to about 1 inch and a length along the top edge in therange from about 1 foot to about 3 feet, for example. Blade 40 shouldhave enough length to insure that an object will not snare under acorner of the covering even if the seafloor is uneven or there arevariations in hardness of the seafloor at different areas under bottomhorizontal members 16 of covering 10 that cause blades at differentcorners to penetrate different distances into the seafloor. Blade 40 ispreferably rounded such that a net would be less likely to hang ifcontacting the end of the blade.

[0022]FIG. 5 illustrates a method for installing protective covering 10on seafloor 62 over protrusion 64 of a subsea well. Protrusion 64 may becasing, a wellhead, mudline suspension or any other equipment. Normally,protrusion 64 will be a stub of 30-inch diameter casing. Preferably, thecasing will contain corrosion cap 65, which has previously been set inthe casing by well known techniques. Corrosion cap 65 may have stripesor other pattern painted on the upper surface so that it can be moreeasily seen with television camera 68. Drill pipe 60, deployed from rig55, may be used to lower covering 10 to the seafloor. Bumper sub 66 maybe present in drill pipe 60 to assist in driving blades of bladeassemblies 20 into seafloor 62. Covering 10 may be located overprotrusion 64 by television camera 68 that may be run through drill pipe60 on wireline 70. Wireline 70 is deployed from a reel located on rig55. After covering 10 is positioned and lowered over protrusion 64 toseafloor 62, bumper sub 66 may be operated to drive blade 40 of bladeassembly 20 into the seafloor. Drill pipe 60 is then released fromcovering 10 and retrieved.

[0023] While particular preferred embodiments of the present inventionhave been described, it is not intended that these details should beregarded as limitations upon the present invention, except as and to theextent they are included in the following claims.

What I claim is:
 1. A protective covering for equipment protruding froma subsea location, comprising: a skin, the skin being attached to aplurality of slanted support members, the slanted support membersincluding a plurality of lateral slanted support members and a pluralityof corner slanted support members, the corner slanted support membersbeing disposed at a selected angle of slope and being attached to aplurality of bottom horizontal support members; a cap, the cap beingattached to a selected number of the plurality of slanted supportmembers and having an attachment point for lowering the protectivecovering to a selected seafloor location; and a plurality of blades, theblades being affixed to the corner slanted support members and beingdisposed at a selected angle of slope.
 2. The protective covering ofclaim 1 wherein the number of corner slanted support members is four. 3.The protective covering of claim 1 wherein the attachment point of thecap is adapted to attach to a drill pipe.
 4. The protective covering ofclaim 1 wherein the selected angle of slope of the blades isapproximately the angle of slope of the corner slanted support members.5. The protective covering of claim 1 wherein the blades include slopingsurfaces disposed so as to improve penetration of the blades into aseafloor.
 6. The protective covering of claim 1 wherein a selectednumber of the plurality of lateral support members and bottom horizontalsupport members are joined such that they may be divided and re-joinedby a joining apparatus.
 7. The protective covering of claim 6 whereinthe joining apparatus is a flange.
 8. A method for installing aprotective covering having a plurality of corner slanted support membersover equipment protruding from a seafloor location, comprising:attaching a plurality of blades to the protective covering, the bladesextending below the plurality of corner slanted support members;attaching the protective covering to a drill pipe operated from a rig;lowering the drill pipe and protective covering; and guiding theprotective covering over the equipment protruding from the seafloorlocation and landing the protective covering on the seafloor location.9. The method of claim 8 wherein the step of guiding the protectivecovering over the equipment protruding from the seafloor locationincludes placing a television camera through the drill pipe andobserving the equipment protruding from the seafloor location while thedrill pipe and protective covering are lowered.
 10. The method of claim9 further comprising the step of placing a pattern on the equipmentprotruding from the seafloor location for observation with thetelevision camera before the step of guiding the protective coveringover the equipment protruding from the seafloor location.
 11. The methodof claim 8 further comprising the step of operating a bumper sub afterthe after the step of landing the protective covering on the seafloorlocation.
 12. A method for installing a protective covering having aplurality of corner slanted support members over equipment protrudingfrom a seafloor location, comprising: attaching a plurality of blades tothe protective covering, the blades extending below the plurality ofcorner slanted support members; attaching the protective covering to acable operated above the seafloor location; lowering the cable andprotective covering; and guiding the protective covering over theequipment protruding from the seafloor location and landing theprotective covering on the seafloor location.
 13. A method fortransporting a protective covering for equipment protruding from aseafloor location, the protective covering comprising a skin, aplurality of slanted support members including a plurality of lateralslanted support members and a plurality of corner slanted supportmembers, at least two contiguous lateral slanted support members beingjoined such that they may be divided at a plane and re-joined by ajoining apparatus, the corner slanted support members being disposed ata selected angle of slope and being attached to a plurality of bottomhorizontal support members, at least two contiguous bottom horizontalsupport members being joined such that they may be divided at the planeand re-joined by a joining apparatus, a cap and a plurality of blades,comprising: dividing at least two contiguous lateral slanted supportmembers and two bottom horizontal support members at the plane andtransporting the protective covering to a selected location; re-joiningthe contiguous lateral slanted support members and the contiguous bottomhorizontal support members at the plane; attaching the skin and the capto a plurality of slanted support members; and attaching the blades.